LOCal Oxidation of Silicon (LOCOS) is a semiconductor fabrication process that uses a patterned oxygen diffusion barrier layer, commonly a silicon nitride layer over areas not meant to be oxidized, where a thermally grown silicon dioxide layer is formed in etched apertures in the oxygen diffusion barrier layer at a given thickness, with a thinner tapered silicon oxide region being formed along the edges of the oxygen diffusion barrier layer. A Si-silicon oxide interface is formed at a lower point than the rest of the silicon surface. Some capacitors utilize a LOCOS oxide as their dielectric. Although the active areas widths bordered by a LOCOS oxide can be varied, LOCOS like other oxide growth processes provide a single given oxide thickness across the die and across the wafer.